1. Field of the Invention
This invention relates to the location of buried objects utilizing electromagnetic induction techniques.
2. Description of Related Art
In a paper entitled "Determination Of Depth Of Shallowly Buried Objects By Electromagnetic Induction", IEEE Transactions on Geoscience and Remote Sensing, Vol. GE23, No. 1, January 1985, bas, McFee and Chesney, the authors describe a method of determining the depth of a shallowly buried metallic object, or targets utilizing a transmitter coil in a plane parallel to and above terrain to be investigated and two receiver coils in spaced planes parallel to the transmitter plane and above terrain to be investigated, an electrical current in the transmitter coil being controlled to apply a pulsed magnetic field to the terrain and the transient response of the receiver coils being monitored; the different amplitude response of the receiver coils to a detected anomaly permits the depth of the anomaly to be determined. The theoretical basis of this technique and its experimental verification are set forth in the paper and will not be repeated here. We have successfully constructed and tested portable apparatus embodying the technique; by transporting the apparatus in repeated spaced passes over an area of terrain, it is possible to map targets buried in the terrain.
In many cases, the accuracy and information content of a map so produced can be prejudiced by presence of multiple superposed targets: most often the problem arises from nearby surface conductors which provide strong responses which can mask that of more deeply buried targets, but problems can also arise from large, highly conductive objects underlying intended targets such as might occur in searching for unexploded ordnance.